1. Field of the Invention
This invention relates, in general, to circuit breakers, and more particularly to circuit breakers having a resistor in parallel with a contact thereof.
2. Description of the Prior Art
Recently a circuit breaker for ultra-high voltage use, for example 500 KV use, having a resistor in parallel with a contact thereof has been used. This circuit breaker is able to suppress an overvoltage generated in the electric power system when the contact is closed by inserting the resistor in parallel with the contact for a short time such as, for example about 10 milliseconds (hereinafter abbreviated as ms) before its closing. However for a circuit breaker for higher voltage use, such as 1000 KV use, it is necessary to suppress an overvoltage generated in the electric power system not only when the contact of the circuit breaker is closed but also when it is opened.
A circuit breaker, such as a compressed air circuit breaker, is known in which a resistor is provided in parallel with a main contact in order not to suppress an overvoltage but to be broken easily. In this circuit breaker, there are provided two separate driving devices: one for use by a main contact and one for use by a resistor contact. However, it is very difficult from an economic standpoint to provide two separate driving devices which need very high power for operation and two separate coupling devices for coupling the main contact or the resistor contact with the driving devices in a circuit breaker for use at ultra-high voltages.